Cannot reinstall theme in Appearance preferences

[Papex]

Actually I've got two issues here:

1) I installed a downloaded theme from Gnome-look simply by dragging the downloaded tar.gz file over to Appearance preferences. So far so good.. Then I deleted the theme from Appearance preferences. Now when I try to re-drag it to install it again I get the message "Can't move directory over directory", which kind of indicates to me (I'm new to Ubuntu) that the theme somehow is still there. Anyway I can't re-install it. What do I do?

2) which brings me to my next question: Is there any way to reset or re-install the original Human Theme? Not that I like it that much, but I installed the Kubuntu-Desktop and tried it once. After I switched back to Gnome I still have the KDE pointer and when I try to go into Appearance Preferences I am unable to choose the Human pointer. I can choose other pointers like "DMZ" or "whiteglass" but there's just an empty space next to "Human".

Any ideas?

[wasd591]

Let's try going to the main themes folder.
Goto my computer (Places > My Computer) and click My Filesystem, then click on home. If you don't see a folder called .themes, press Ctrl + H. If you still don't see it then reply. If you do, double click and delete the folder with the theme inside it. Then restart and try installing it again.